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What To Know About SMA Prenatal Testing and Diagnosis

Posted on April 20, 2022
Medically reviewed by
Evelyn O. Berman, M.D.
Article written by
Eli Sachse, RN

Are you an expecting parent who has a family history of spinal muscular atrophy (SMA) or a family member who is a known carrier? If so, you may have been advised to consider prenatal genetic testing for your baby. There are many important considerations and decisions to make regarding genetic testing, and each family’s situation is unique.

Who Should Consider Genetic Testing?

SMA is an autosomal recessive condition. That means that it is a genetic disorder that can be passed from parents to their children. However, the parents do not necessarily need to have the condition themselves to pass it on. Parents not affected by a genetic condition they pass on are called carriers.

People with SMA in their family, or people with known carriers in their family, may be referred to genetic counseling for advice regarding genetic testing. Genetic testing for potential carriers of SMA can be done by a simple blood test. A genetic counselor can discuss the likelihood of potential parents passing on SMA to their children.

Genetic testing of potential parents is not 100 percent accurate in predicting if they will pass on the genes that cause SMA. However, depending on your results, your genetic counselor will be able to give you probabilities about potentially passing on the condition and provide advice and options.

If both parents test positive for the gene that causes SMA, and one is already pregnant, they may be advised to undergo genetic prenatal testing of their baby.

Learn more about the genetics of SMA.

Types of Genetic Prenatal Testing

The two main types of prenatal screening for SMA are amniocentesis and chorionic villus sampling (CVS).

Chorionic Villus Sampling

CVS can be done after the 10th week of pregnancy, so it can be the first choice for those who want a diagnosis as soon as possible. CVS can be performed like a Pap test, through the cervix, or by inserting a needle directly through the abdomen. CVS takes a sample of cells from a specific part of the placenta. The child’s DNA can then be extracted from this sample and tested for the genes that cause SMA.

Amniocentesis

Amniocentesis is performed by extracting amniotic fluid (the fluid surrounding the baby) with a needle inserted directly through the parent’s abdomen. It can be performed 15 weeks or later into a pregnancy. The needle is not meant to touch the baby, however, there is a risk of infection as well as miscarriage associated with the procedure. DNA from the baby is then extracted from this fluid for testing.

Risks of Prenatal Testing

There is a risk of miscarriage associated with both of these kinds of diagnostic testing. For amniocentesis, the risk is about 1 in 200. For CVS, the risk is about 1 in 100. For any type of invasive procedure (one that breaks the skin), there is the possibility of infection or poor wound healing. Your health care team will take into consideration your health profile in helping you decide whether genetic prenatal testing is the right choice for you.

There is no right answer in choosing whether or not to get you or your baby tested. Families can choose or decline testing for personal, cultural, or religious reasons.

Next Steps and Support

Families whose unborn baby has tested positive for SMA have a lot to learn and carefully consider. Keep in mind that there are several different types of SMA, with varying degrees of severity. Life expectancy can range from a few years to a normal lifespan. SMA treatments have been available for only a few years now, so it’s unknown how much they may reduce the severity of symptoms in the long term or extend life expectancy.

The degree of disability also varies: For some, it’s severe and starts early in life; for others, it’s mild and develops later on. Unfortunately, the type of SMA a child will develop cannot yet be diagnosed prenatally.

Decisions around family planning are intensely personal. Some families may choose to terminate a pregnancy and consider starting or growing their family with different fertility options, or adoption.

Families choosing to continue the pregnancy should reach out to their primary care provider and OB-GYN to make sure they’ve been informed of the test results. Because SMA is very rare, your health care team may need to educate themselves about the condition and be prepared to provide support.

Several national organizations can provide support in a variety of ways, including:

Talk With Others Who Understand

On mySMAteam, the social network for people with SMA and their loved ones, more than 1,500 members come together to ask questions, give advice, and share their stories with others who understand life with SMA.

Have you chosen prenatal genetic testing for your family? Share your experience in the comments below, or start a conversation by posting on your Activities page.

All updates must be accompanied by text or a picture.
Evelyn O. Berman, M.D. is a neurology and pediatric specialist and treats disorders of the brain in children. Review provided by VeriMed Healthcare Network. Learn more about her here.
Eli Sachse, RN is a registered nurse living in California. He has written about health topics for Sonoma Medicine and Microcosm Publishing. Learn more about him here.

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